Conventionally, a refrigerator for example as disclosed in Patent Document 1 includes an evaporator, a compressor and a condenser.
Such a refrigerator includes, for example, a compressor shown in FIG. 3 by Patent Document 2. This compressor is a two-stage screw compressor compressing a refrigerant gas such as a CFC gas in two stages and including a pair of first-stage screw rotors 101 and 102 and a pair of second-stage screw rotors 103 and 104, each screw rotor 101 to 104 being housed in a casing 106.
The first-stage screw rotors 101 and 102 engage with each other in a first compression chamber 106a inside of the casing 106 and the second-stage screw rotors 103 and 104 engage with each other in a second compression chamber 106b inside of the casing 106. The rotor shaft of each screw rotor 101 to 104 is supported by each corresponding bearing 108. In the first compression chamber 106a, the first-stage screw rotors 101 and 102 mutually engage and rotate to thereby compress a refrigerant gas in the first stage, the compressed refrigerant gas is leaded to the second compression chamber 106b, and the second-stage screw rotors 103 and 104 there mutually engage and rotate to thereby compress the refrigerant gas in the second stage. After compressed in the second stage, the refrigerant gas is discharged from the compressor.
Each bearing 108 is supplied with a lubricating oil, a part of the supplied lubricating oil is contained in a refrigerant gas and flows inside of the compressor, and is discharged together with the refrigerant gas from the compressor. The refrigerant gas and lubricating oil discharged together are sent to an oil separator 110 and separated there. The separated refrigerant gas is sent to a condenser, while the separated lubricating oil is cooled by an oil cooler 111 and returned to the compressor and supplied again to each bearing 108 after impurities contained therein are removed by an oil filter 112.
Patent Document 1: Japanese Patent Laid-Open Publication No. H9-72619
Patent Document 2: Japanese Patent Laid-Open Publication No. H9-268988